Corrosion beneath a blister with high impedance

In this work, the effect of blisters on the performance of protective coatings was investigated. Artificial blisters were generated by potentiostatic DC polarization of an epoxy-coated aluminum substrate and characterized using optical microscopy, electron microscopy (SEM), scanning electrochemical microscopy, as well as by scanning Kelvin probe (SKP) measurement. Impedance measured above blisters displayed high values, typical of an intact undamaged coating. SKP measurement above the blister identified regions of likely corrosion beneath it, which was verified by SEM. SEM images showed pitting-like corrosion beneath the blisters, implying that high impedance measured on delaminated coatings may correspond to the delaminated polymeric film. SKP was also able to identify regions of invisible delamination.